1. Field of the Invention
The present invention relates to water systems, e.g., closed hot water heating systems, pressurized water systems, and the like, that include expansion tanks or well tanks and, more particularly, to water systems including non-metallic expansion tanks with an internal diaphragm that separates a pressurized air chamber from a water storage chamber.
2. Description of Related Art
Water systems that provide and distribute well water domestically in rural parts of the country typically include a pump to draw water from the well; pipes or other conduits through which water travels; and a tank for storing water, e.g., a well tank. Well tanks, for example, expansion tanks, are structured and arranged to store water until demanded and to accommodate internal pressures of the system. To this end, well tanks typically provide an air cushion for the supply water.
Generally, the water chamber in the interior of the tank assembly that stores water is in fluid communication with the pipes or conduits of the domestic water system. By design, the water chamber is structured and arranged to provide an operating pressure, e.g., about 20 to 40 pounds per square inch (“psi”), to the water system. To accomplish this, the compressible gas chamber contains a pressurized gas, e.g., nitrogen or, more preferably, air, that can force water through the water system and that, further, can prevent creation of negative or back pressures in the water system during the cyclical demand for water and/or volume changes associated with the change in water temperature. If the pressure in the water chamber falls below the operating pressure, the pump is activated and water is added to the water chamber of the expansion tank until the water chamber again provides the operating pressure.
In any closed system containing air and water that undergoes natural or artificial temperature changes, the likelihood of problems stemming from interaction of air and water is great. Air is soluble in water and water readily absorbs air. Indeed, the amount of absorbed air in water is inversely proportional to the water temperature. Thus, as water is heated, e.g., in connection with a closed hot water heating system, the air in the water is liberated into the system and as heated water cools, the cooling heated water in direct contact with air, e.g., in the compression tank, absorbs some of the free air. By its very nature and through thermal circulation, air-charged water that is cyclically heated and cooled changes continually so that during the next heating cycle the re-absorbed air is again liberated into the system. This cyclical and reversible process is repeated as often as the heating, or firing, cycle is repeated and the boiler water is heated and cooled. This poses many problems to designers.
First, air released by heated water, typically, accumulates in the compression tank and other portions of the heating system. This accumulation results in reduced heating efficiency. This makes continuous venting of radiators or convectors to bleed off the air necessary. Moreover, as water is heated, it can expand into the compression tank that is connected to the pipes and other conduits. Typically, in the compression tank, the expanding, heated water is in intimate communication with the released air and any other air in the tank. However, when the heated water reaches a desired temperature, the firing of the boiler ceases and the water begins to cool and contract. As the water cools, it re-adsorbs free air in the compression tank.
Second, when a tank includes an air cushion, the cooling water may absorb all or substantially all of the air cushion, leaving a static water system. Without an air cushion, or, more specifically, air pressure to force water through the system, a pressure pump may be needed constantly. Optionally, an air surge chamber can be provided that is not in direct contact with the water, thereby eliminating the need of the pressure pump operating every time a faucet was turned on. Pressure pumps and surge chambers increase the cost of a water system.
To address these shortcomings, conventional expansion and well tanks (collectively “tank assemblies”) typically include impermeable diaphragms, or bladders, to separate the interior of the well tank into two chambers, or cells: a liquid, or water, chamber and a compressible, or pressurized, gas chamber. As water is pumped from a well into the tank assembly, the volume of water in the water chamber increases. This causes the diaphragm to contract the volume of the pressurized gas chamber.
As the volume of the pressurized gas chamber decreases, the gas pressure in the pressurized gas chamber increases. Consequently, when water for the tank is demanded by the water system, the gas in the pressurized gas chamber forces the water into the water system. As a result, the volume of water in the water chamber decreases, the volume of the pressurized gas chamber increases, and thus the pressure of the pressurized gas decreases.
Conventional diaphragms are constructed of a non-porous, elastic material, e.g., plastic or butyl rubber, and are sealed at the periphery or sidewall of the tank to provide an air- and watertight seal. Not only does the use of a diaphragm avoid the above-described air-water problems, but, also, separation of water from the pressurized gas is desirable because water in the presence of oxygen produces oxidation that can damage metal or other portions of the system and, furthermore, can aerate the water, which can affect water quality.
An example of a conventional tank assembly is provided in U.S. Pat. No. 5,386,925 to Lane. The Lane patent provides an expansion tank comprising a deformable diaphragm that divides the tank into two sections. The diaphragm separates the gas in the one section of the tank from the water in the other section of the tank and the rest of the system. The gas section is pre-charged with gas under pressure so that the diaphragm is displaced to increase or decrease the volume of this section according to the variations of the volume of water in the other section.
The Lane expansion tank system includes two sections that are made of metal, which requires assembly with, i.e., welding to, a metal clamp ring that is disposed inside of the two tank portions. This assembly is relatively expensive and labor and time intensive to manufacture. Moreover, steel tanks can corrode from external environmental exposure, which can lead to deterioration of the tank assembly and the water system. Such deterioration can lead to catastrophic results, such as leaking tanks.
To provide some protection from corrosion, the inner surface of the liquid chamber portion of the metal expansion tank is covered by a water, or liquid impervious liner. This, however, requires fabricating the liner in a separate operation and then inserting the liner in the liquid chamber portion.
Therefore, it would be desirable to provide a non-metallic tank assembly that does not affect the quality or taste of the water or that does not deteriorate over time in a corrosive environment. It would also be desirable to provide a non-metallic tank assembly with an internal diaphragm interposed between the water chamber and the gas chamber to separate the water from pressurized gas. Furthermore, it would be desirable to provide a non-metallic, diaphragm-type tank assembly that can withstand the internal pressures normally associated with tank assemblies. Finally, it would be desirable to provide a lighter, non-metallic alternative to conventional metallic tank assemblies and to provide such a tank at lower cost.